The present invention relates generally to a interference cancelers, and more particularly, to an adaptive cross polarization interference canceler for use at intermediate frequencies.
In satellite communications the quest for ever increasing data rate limited bandwidth has led to the reuse of frequencies through polarization diversity. Under certain adverse conditions this reuse of frequencies requires the use of an adaptive cross polarization interference canceler. Since the interfering cross polarization signal might be distorted by dispersion, a compensating transversal filter is sometimes included in the cancellation path of the adaptive cross polarization interference canceler.
A search was performed that uncovered a number of prior art patents that are only generally related to the present invention. The present intermediate frequency adaptive cross polarization interference canceler differs from these prior art patents as indicated below.
The intermediate frequency adaptive cross polarization interference canceler is not an adaptive filter. In particular, the interference canceler always processes two signals not one. The prior art patents relating to adaptive filters include U.S. Pat. No. 4,453,256, U.S. Pat. No. 5,228,060, U.S. Pat. No. 3,659,229, U.S. Pat. No. 4,271,525, U.S. Pat. No. 4,760,596, U.S. Pat. No. 4,691,176, U.S. Pat. No. 3,878,468, U.S. Pat. No. 4,422,175, U.S. Pat. No. 5,278,780, U.S. Pat. No. 4,731,834, U.S. Pat. No. 4,320,526, U.S. Pat. No. 5,282,023, U.S. Pat. No. 5,311,546, U.S. Pat. No. 4,097,807, U.S. Pat. No. 5,285,482, U.S. Pat. No. 5,418,816, U.S. Pat. No. 5,394,110, U.S. Pat. No. 4,562,312, U.S. Pat. No. 4,281,411, U.S. Pat. No. 4,513,429, U.S. Pat. No. 4,594,725, U.S. Pat. No. 5,228,058, U.S. Pat. No. 5,036,525, U.S. Pat. No. 4,742,510, U.S. Pat. No. 5,311,558, U.S. Pat. No. 3,715,670, U.S. Pat. No. 5,481,564, and U.S. Pat. No. 5,442,582.
The present intermediate frequency adaptive cross polarization interference canceler and its adaptive control are completely self-contained and independent from the rest of the receiver. This means that adaptation can commence before signal acquisition, which shortens the total acquisition time considerably, which is an important feature when the canceler is used in a satellite modem application. The referenced circuits, which are different from the present invention and which are dependent on another portion of the receiver include U.S. Pat. No. 5,383,224, U.S. Pat. No. 4,914,676, U.S. Pat. No. 4,992,798, U.S. Pat. No. 5,432,522, U.S. Pat. No. 5,075,697, U.S. Pat. No. 5,442,663, U.S. Pat. No. 4,910,468, U.S. Pat. No. 5,327,458, U.S. Pat. No. 5,272,663, U.S. Pat. No. 4,283,795, U.S. Pat. No. 5,406,589, U.S. Pat. No. 4,701,935, U.S. Pat. No. 4,664,562, and U.S. Pat. No. 4,146,893.
Other prior art patents found in the search address a large variety of subjects that are not related to the present intermediate frequency adaptive cross polarization interference canceler in a variety of ways. These patents include U.S. Pat. No. 4,947,361 which deals with CW interference only. U.S. Pat. No. 5,084,902 cancels jitter due to very low frequency interference. U.S. Pat. No. 5,440,308 requires prior knowledge about the nature of the interference. U.S. Pat. No. 4,631,734 requires external computational resources. U.S. Pat. No. 4,293,945 only measures the depolarization, but does nothing about it. U.S. Pat. No. 4,320,535 requires external computational resources. U.S. Pat. No. 4,191,926 deals only with constant envelope signals. U.S. Pat. No. 4,369,519 deals with compensation not cancellation.
Accordingly, it is an objective of the present invention to provide for an adaptive cross polarization interference canceler for use at intermediate frequencies that is particularly well suited for use in satellite modems, and the like.